The morphogenesis of biological tissue involves the organization of cells into functional, self-assembled structures [1]}. The aggregation of cells into ordered structures requires effectively attractive cell-cell interactions [2]}. An example that is significant for biological development, disease and tissue engineering, is the morphogenesis of blood vessels. This is initiated by patterned structures of endothelial cells (ECs), which align end to end to form elongated chains that intersect to give a branched morphology. Although the conditions required for vascular-like development in engineered in vitro systems are well established and EC vascular networks have been mathematically modeled using various approaches [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, the nature of the cell-cell interactions that drive the ECs to find each other to form networks, and the dependence of these interactions on matrix stiffness, have not been definitively identified.
